An effective oral composition can maintain and preserve tooth appearance by removing dental stains and polishing the teeth. It may clean and remove external debris as well, which can aid the prevention of tooth decay and promote gingival health.
Abrasives in oral compositions aid in the removal of the tightly adherent pellicle film to which dental stains affix. Pellicle film usually comprises a thin acellular, glycoprotein-mucoprotein coating, which adheres to the enamel within minutes after teeth are cleaned. The presence of various food pigments lodged within the film accounts for most instances of teeth discoloration. An abrasive may remove the pellicle film with minimal abrasive damage to oral tissue, such as the dentin and enamel.
In addition to cleaning, it may be desirable for abrasive systems to provide polishing of tooth surfaces, as polished surfaces may be more resistant to ectopic deposition of undesirable components. Tooth appearance may be improved by imparting a polished character to the teeth, because the surface roughness, that is, its polish, affects light reflectance and scattering, which integrally relate to the teeth's visual appearance. The surface roughness also affects tooth feel. For example, polished teeth have a clean, smooth, and slick feel.
Numerous dentifrice compositions use precipitated silicas as abrasives. Precipitated silicas are noted and described in U.S. Pat. No. 4,340,583, Jul. 20, 1982, to Wason, EP Patent 535,943A1, Apr. 7, 1993, to McKeown et al., PCT Application WO 92/02454, Feb. 20, 1992 to McKeown et al., U.S. Pat. No. 5,603,920, Feb. 18, 1997, and U.S. Pat. No. 5,716,601, Feb. 10, 1998, both to Rice, and U.S. Pat. No. 6,740,311, May 25, 2004 to White et al.
While providing effective cleaning of teeth, precipitated silicas in oral compositions may present compatibility problems with key formula actives, such as stannous ions. These compatibility problems have been shown to be directly related to surface properties of precipitated silicas such as surface area, number of hydroxyl groups, and porosity.
PCT Published Patent Application WO 93/23007 assigned to W. R. Grace discloses that thermal treatment of precipitated silica at 300-850° C. for 1-3 hours can significantly improve compatibility with CPC or chlorhexidine. Reference is also made to non-fluoride therapeutic agents.
U.S. Pat. No. 4,346,071 (PQ Corp-8/24/87) discloses improved abrasivity by dehydrating then rehydrating silica gel. The silica gel therein was heated to 310° C.
A need exists for an abrasive system that has good compatibility with stannous ions while providing effective and safe cleaning and polishing of dental tissue. In addition, there exists a continuing need for abrasives that can produce superior cleaning and polishing at reduced costs. The methods and compositions of the present invention related to the heat treatment of precipitated silica particles may provide one or more of these advantages. The present invention also relates to oral compositions containing improved precipitated silica particles and methods using such oral compositions that may provide better stannous stability.